Conventional photodiodes transform light into an electric current or voltage at a pn-junction or pin-junction. Depending on the specific pn-junction, the light, which more generally can be considered as an electromagnetic wave, may be of ultraviolet or infrared or visible frequency spectrum. For transforming light of different wavelength a photodiode may comprise silicon for detecting visible light in the range of up to 1 μm or may comprise germanium for detecting light in the infrared spectrum for up to 1.8 μm or other conventional semiconducting materials for transforming light into current or voltage.
When the photosensitive pn-junction is exposed to light, the incident photons generate pairs comprising a mobile electron and a corresponding positively charged hole, thus producing a current flow, as the charge carriers move into the zones of opposite doping due to the diffusion voltage. For affecting a pair of an electron and a hole, the photons necessarily must yield an energy exceeding the band gap of the particular photosensitive pn-junction. The current affected by the impinging photons to a large extent is proportional to the amount of energy comprised in the photons until saturation is encountered.
Photodiodes can be used in a variety of circuits, wherein the photodiodes exhibit different properties. In one embodiment, when the photodiode is operated without any bias, the current flow out of the diode is limited and a voltage builds up, the diode thus becoming forward biased. This causes a so-called dark-current flowing in an opposite direction to the photo current and which in the end causes the photovoltaic effect in solar cells. In another embodiment, the so-called photoconductive mode, a reverse bias may be applied, which decreases the capacitance of the pn-junction and reduces the response time of the diode. In still another embodiment a comparatively high reverse bias may be applied to the diode, which affects a multiplication of each charge carrier by the avalanche effect, thus affecting an internal gain in the photodiode.
Photodiodes are used in a variety of applications, for example, in consumer electronics or any other application wherein light must be detected. In some particular applications polarizers have been used for preventing light of a dedicated polarization to pass through the polarizer and to affect a corresponding current or voltage in the photodiode. In one embodiment, polarizers have been used in combination with photodiodes to differentiate between lights of differing polarization.
The polarizers used in these conventional photodiodes are discrete polarizers. That is, the polarizers are made of glass or transparent plastics in a standalone production process, which is separate from the production process of producing a semiconductor. In other words, the process is separate from producing a photodiode as a conventional semiconductor using conventional semiconductor production methods. When the polarizers were produced they were placed in front of the photosensitive material of the photodiode. The production of these photodiodes accordingly comprises the production of the polarizer and a photo diode, both as separate items, and as a micromechanical assembly of the polarizer in front of the photosensitive area of the diode. As micromechanical assemblies are costly and prone to errors, there is a need for an alternative.